Field of the Invention
The present invention relates to vapor-liquid contact tower having a structured packing bed, the structured packing bed including a plurality of packing layers, the packing layers include a plurality of corrugated sheets and, more particularly, but not by way of limitation, corrugated contact sheets or plates having upper and lower linear corrugated fluid flow interface regions, each linear corrugated fluid flow interface region being disposed at an angle relative to intermediate corrugated body portions, at least some linear corrugated fluid flow interface regions abutting contiguous linear corrugated fluid flow interface regions of a second vertically-adjacent packing section to enhance fluid flow therebetween.
History of the Related Art
In the vapor-liquid tower contact art, it is highly desirable to efficiently improve the quality as well as the quantity of the mass heat transfer occurring in process towers during fluid flow therethrough. The technology of such process towers is replete with various material designs used for tower packing. Types of packing as well as packing designs are dependent on the particular process to be effected within the tower. The packing elements may thus comprise a structured grid array (grid packing) arranged to form a regular array inside the column or may comprise oblique shapes dumped into and randomly arranged (dump packing) or structured packing within the tower. Close fractionation and/or separation of the feed stock constituents introduced into the tower and the elimination of harmful or undesirable residual elements imparts criticality to the particular vapor-liquid contact apparatus placed within the tower. In particular, the shape of the grid, dump, or grid packing elements generally determines the flow patterns in and density of the array and the resultant resistance to fluid flow caused thereby.
It has been found particularly desirable to afford efficient heat transfer, fluid vaporization, or vapor condensation whereby cooling of one of the fluids can be accomplished with a minimum pressure drop through a given zone of minimum dimensions. High efficiency, low pressure drop, and reduced temperatures are most often found as design criteria in the chemical-engineering art as applied to petroleum fractionating operations. Process towers for effecting such chemical reactions are generally of the counter-current flow type providing descending fluid flow from an upper portion of the tower and ascending fluid flow from a lower portion of the tower. In some instances, the ascending fluid flow may be in the vapor phase. With ascending vapor flow, sufficient surficial area for vapor-liquid contact is necessary for the primary function and the reduction or elimination of liquid entrainment present in the ascending vapor. Most often it is necessary for the packing array to have sufficient mass and surficial area in both its horizontal and vertical planes so that fractions of the heavy constituents are conducted downwardly in condensed form and the vapors are permitted to rise through the packing with minimum impedance. With such an apparatus, undesirable solids or heavy constituents of the feed stock are removed by the coaction of the ascending liquid vapor to provide some self-cleaning with the grid. A plurality of stacked layers affording compatible and complemental design configurations are generally assembled within a single process column. Each layer utilizes the velocity and kinetic energy of the ascending vapors to perform the dual function of eliminating liquid entrainment in the ascending vapor and the thorough and turbulent contacting of the vapor with the descending liquid to accomplish sufficient separation or fractionation of the fluids into desired components. Quick cooling of the ascending vapor is generally a prerequisite for efficient operation to effect efficient heat transfer for vapor condensation and minimum pressure drop in a minimum vertical depth of the packing. Oppositely inclined corrugated lamella, also referred to as sheets or plates, have thus been utilized in the prior art for affording multiple vapor passages through the horizontal and vertical planes of the packing layers to insure the flow of vapor and distribution thereof within the lamella and prevent maldistribution, or channeling, of the vapor through certain portion of the layers and not others. Only in this manner is efficient and effective utilization of the column and the energies applied therein effected.
Most often used in process columns is a plurality of layers with packing members of each layer having angularly disposed adjacent elements. Each element generally has a structural configuration and angularity that permits a large upright vapor passage area which is in excess of one-half the horizontal area of the lamella. This design affords acceptable efficiency and vapor-liquid distribution for heat-mass transfer. Such structures also be necessity provide thorough and turbulent mixing or contacting of ascending vapor and descending liquid. This is done without materially displacing either the vapor or liquid from its vertical location within the flow grid. It is important to prevent maldistribution or channeling of either the vapor or the liquid through certain portions of the packing or its layers.
The structural configuration of inclined corrugated contact plates variety often incorporate linear vapor orifice passages. Vapor turbulence is created by such orifices to insure intimate vapor liquid contact. It is also necessary to insure the ascending vapor performs a dual function of liquid contact and liquid disentrainment within close proximity to the vertical location at which ascending vapor approaches or leaves the vapor passage orifices. In this manner maldistribution of ascending vapor or descending vapor is prevented.
Oppositely-inclined corrugated plates provide but one method and apparatus for countercurrent, liquid-vapor interaction. With such packing arrays, the liquid introduced at or near the top of the column and withdrawn at the bottom is effectively engaged by vapor being introduced at or near the bottom of the column and withdrawn at the top. In such methods and apparatus it is necessary to insure that the liquid and vapor achieve the desired degree of contact with each other so that the planned reaction or separation occurs at a designed rate within controlled parameters of mass transfer. The internal structure is, of course, passive in the sense that it is not power driven and has few, if any, moving parts. Common devices utilize cross-fluted and perforated sheets of material in face-to-face engagement. This configuration encourages the liquid moving through the packing to form itself into films having, in the aggregate, a large area over which the vapor may pass. However, the design problem is not merely a matter of providing a large surface area or a multitude of corrugations, cross-flutes, or perforations. A number of other interrelated design considerations must be taken into account, some of which have been mentioned above.
From a process standpoint, it is important that the desired vapor-liquid contact reaction be carried as close to completion as possible. For example, in a crude oil vacuum tower, close fractionation and good separation are needed to produce gas oil streams that are free of undesirable residual elements. As mentioned above, the contact column and its internal apparatus must efficiently utilize the heat supplied to the unit. In this manner, it minimizes direct operating costs, whether the reaction is mass transfer, heat transfer, liquid-vaporization or vapor condensing duty. With the above, pressure drop is the primary consideration as is the vapor-liquid fluid interface. U.S. Pat. No. 4,842,778, issued Jun. 27, 1989, for example, discusses a structured packing section having corrugated layers of one half to one third of conventional thickness for improving vapor-liquid interaction. U.S. Pat. No. 6,206,349, reexamination certificate issued Oct. 11, 2011, discusses packing sheets having a progressively varying crimp angle in the region of sheet interface. U.S. Pat. No. 5,124,087, issued Jun. 23, 1992, discusses packing sheets having a bottom edge that is cut on an oblique angle along the width of the packing sheet. U.S. Pat. No. 6,478,290, issued Nov. 12, 2002, discusses a packing section having a base region, a bulk region, and a top region. Each of the base region, the bulk region, and the top region has a particular geometry that is different from the other two regions.
In the above-referenced vapor-liquid contact method and apparatus patents, a plurality of design configurations are presented for affording intimate vapor-liquid contact. In particular, stacked corrugated contact plates in face-to-face contact having corrugations inclined to the horizontal, and/or orthogonal one to the other, have been shown and provided in various material configurations. These configurations include monofilament yarns, and solid plates.
While many prior art methods and apparatus for vapor liquid contact have been shown to be effective, certain disadvantages still remain. In particular, vapor-liquid contact towers incorporating descending liquid flow and ascending vapor flow of the structured packing variety defined above, is generally incapable of self-regulation of internal pressure differentials and the prevention of maldistribution, or non-homogenous, vapor-liquid flow across the grid areas. This is true even with a plurality of apertures disposed between corrugated and/or cross-fluted plates in face-to-fact contact. Vapor flow is ultimately sensitive to pressure differentials, including laminar flow patterns, and is easily diverted between the myriad of exposed areas of mating corrugations or flutes. When the corrugations of adjacent plates are inclined at relatively sharp angles, vapor flowing along any one corrugation may be substantially exposed to the adjacent corrugated channels rather than to the film of liquid along wall sections. Vapor-liquid flow in such configurations is thus susceptible to an inefficient, random flow pattern which cannot be accurately determined within the passive contact plates. Likewise, when corrugations of adjacent plates are inclined at relatively flat angles, vapor flowing along any one corrugation is susceptible to a high degree of pressure drop, which pressure drop inhibits fluid interaction and decreases efficiency.
Additionally, fluid flow through vertically-aligned structured packing sections is particularly important at an interface between two adjacent vertically-aligned structured packing sections. At the interface, fluid flow is susceptible to high pressure drop, random flow patterns, and decreased fluid interaction and efficiency. As will be discussed hereinbelow, the present invention facilitates decreased pressure drop at the interface by having corrugations interface at steep angles. However, by having the respective corrugations interface at angles between 15 degrees and 7 degrees from vertical, the present invention also facilitates laminar fluid flow along the corrugations thereby enhancing fluid interaction and improving efficiency.